Corrosion Behavior of Cr, Fe and Ni Based Superalloy in Molten NaCl

Abstract Molten NaCl is a strong corrosive substance for its container when NaCl acts as solar high-temperature phase change thermal storage medium. The corrosion kinetics curves were measured and drawn by means of a 192 h corrosion experiment of Fe, Cr, Ni-base alloys in 850 °C molten NaCl. The cross section characteristics, the elements distribution features and the corrosion products of the samples were analyzed after corrosion by SEM, EPMA, EDS and XRD, and the corrosion mechanism was studied. The results show that the corrosion kinetics curves of three kinds of the alloys obey the linear law, the acceleration of mass loss rate for the three kinds of a alloys can be attributed to the reactions among chromium and NaCl, etc. Chromium based alloy shows the worst corrosion resistance among the three alloys, with the characteristic of corroding along grain boundaries (which provide channels for the infiltration of molten NaCl to alloy matrix), hence the corrosion process is accelerated. A thicker corrosion layers are formed on the surfaces of the nickel based and the iron based alloys, which provide a foundation for the adherence of Cr 2 O 3 . The adherence of Cr 2 O 3 can lower the driving force of the Cr diffusion, which improves the corrosion resistance of the alloy. In addition, a spinel structure layer of corrosion product is formed on the surface of the iron based alloy, which improves the iron based alloy corrosion resistance ulteriorly, and makes it perform the best corrosion resistance among the three alloys.